This invention relates to the production of concrete expansion joints. It was designed specifically as an inexpensive joint structure for residential concrete projects.
The need for expansion joints in concrete slabs, walks and drives in residential projects is well recognized. However, while rather complicated and expensive joint structures are available for commercial projects, most small projects and residential work utilize rather crude and ineffective joints. For example, wood boards are often used to produce a joint. While wood is initially attractive, it expands by absorbing water from the wet concrete and then contracts as it subsequently dries. This leaves a void space where the wood abuts the concrete at its side surfaces. Surface water can seep through this space, which destroys the joint and erodes the subgrade beneath the concrete.
Felt is another material used with varying degrees of success as a joint material. It also shrinks and allows gaps to be created between the joint and concrete. Furthermore, it is very difficult to hold in a straight condition and is generally recognized as being unsightly because of its incompatibility with concrete and concrete-forming methods.
Both wood and felt make edging with a metal tool very difficult. Both materials swell in contact with wet concrete and create a very tight edging surface.
Metal and concrete make joints that are both effective and attractive. Metal not only provides controlled expansion and cracking in the concrete, but further adds strength to the concrete slab itself. The present structure for forming expansion joints presents a central trough and a pair of oppositely facing side troughs. It can be used with the central trough inverted over supports, or with the central trough facing upwardly to receive a board or other decorative joint material. In either instance, a positive interlock is provided between the metal strip and the concrete slabs at each side of the joint, and a longitudinal trough is provided to receive and direct water along the length of the joint. The joint provides for expansion and contraction of the concrete, as well as for directing water to the edges of the slab.